The invention relates to a turbine ring assembly for a turbomachine, which assembly comprises a ring support structure and a plurality of ring sectors, each comprising a single piece of ceramic matrix composite material.
The field of application of the invention is particularly that of gas turbine aeroengines. Nevertheless, the invention is applicable to other turbomachines, e.g. industrial turbines.
Ceramic matrix composite (CMC) materials are known for their good mechanical properties, which make them suitable for constituting structural elements, and for their capacity to conserve those properties at high temperatures.
In gas turbine aeroengines, improving efficiency and reducing polluting emissions are leading pursuit of ever-higher operating temperatures.
Thus, the use of CMCs for various hot portions of such engines has already been envisaged, particularly since CMCs present density that is less than that of the refractory metals that are conventionally used.
Thus, making one-piece CMC turbine ring sectors is already described in document U.S. Pat. No. 6,932,566. The ring sectors have a K-shaped meridian section with an annular base in which the inside face defines the inside face of the turbine ring and an outside face from which there extend two tab-forming portions with ends that are engaged in U-shaped housings in a metal structure for supporting the ring. The tabs have their ends engaged with radial clearance in the U-shaped housings and they are held to bear radially against surfaces of the housings by means of a resilient member that exerts a return force on the ring sector, which force is directed radially towards the axis of the ring.
Engaging the ends of the tabs in the housings with clearance makes it possible to accommodate differential expansion between the CMC and the metal of the ring support structure, however the resilient mounting presents several drawbacks.
Thus, such resilient mounting is poorly compatible with the finishing machining that is conventionally performed after initial mounting of the ring sectors in order to confer an almost perfect cylindrical shape to the inside surface of the ring.
In addition, when the tip of a blade on a rotor wheel surrounded by the ring comes into contact with an abradable coating present on its inside face, the resilient mounting gives rise to an undesirable vibratory phenomenon.
Furthermore, the sealing of the gas flow passage on the inside of the ring sectors relative to the outside of the ring sectors is affected.